Processes exist to selectively deposit tungsten utilizing disilane (Si2H6) and tungsten hexafluoride (WF6) as precursors. U.S. Pat. No. 8,956,971 to Haukka et al. discloses such a process, where the deposition takes place at approximately a temperature of 150° C. The deposition may result in a tungsten layer being formed over a copper surface.
Approaches to form tungsten via plasma have not been viable due to plasma's adverse effect on the selectivity. Specifically, plasma tends to form films on multiple surfaces, and does not discriminate between the different surfaces.
Formation of tungsten films may be used to improve electromigration (EM) resistance. The EM resistance may be achieved by forming a metal cap over an interface between a dielectric diffusion barrier and a metallic material. However, achieving good selectivity on metallic surfaces versus the dielectric surface has been difficult. Several approaches have been taken, such as gentle surface treatments comprising thermal or radical treatments, in order to obtain the desired surface terminations. The gentle surface treatments, however, may not adequately prepare the desired surface for selective deposition.
As a result, a process is desired that deposits a tungsten or other metal film with a high selectivity.